There are only a few standard parts that need to be understood to make a toilet operate normally. Basically, toilet plumbing is a four step process. The flush handle on the outside of a toilet is connected to a chain inside the tank. This chain is connected to a “flapper” on the tank’s bottom. The first step begins when the handle is pushed down and the chain pulls the flapper up. This releases the water from the tank and sends it to the toilet bowl. With me so far?
Okay, the next step occurs when the toilet’s tank empties its water into the toilet bowl. This water performs a dual function. First, it pushes the dirty water and waste out of the bowl and into a pipe leading to the sewer or septic tank. Second, it refills the bowl with clean water. After this, the flapper again seals the passage of water from tank to bowl and the tank begins filling back up in preparation for the next flush.
The last two steps are carried out differently depending on the age of the toilet plumbing. The third step is refilling the tank, the fourth is stopping that refilling at the right moment. After a flush, the tank is empty and new water begins flowing in. In a conventional toilet, there is a float that sets this process in motion. The emptied tank causes the float to sink and rest at the bottom. The change in position of the float opens a valve (called a ball-cock), which allows clean water to run into the tank. As the tank fills, the float rises to its original position. When it hits that position, the ball-cock closes. The water stops flowing into the tank, and the toilet is ready for the next flush.
Newer toilets don’t have a float. The ball-cock itself is sensitive to water pressure. It opens to send new water into the tank after a flush (when the tank is empty and there is no water pressure). It closes when the water level hits a specified point (when the tank is full and water pressure is high).